Valve drive adjustment devices in internal combustion engines for motor vehicles are known in a variety of applications. Three are mentioned here by way of example. In the case of the “Valvetronic” adjustment device (BMW), an actuating mechanism arranged between a camshaft and a valve tappet is adjusted by means of an electric actuating motor and an eccentric shaft in order to realize a variable (maximum) valve lift as a function of certain operating parameters of the internal combustion engine. Said adjustment of the valve lift may be combined with a so-called camshaft phase adjustment in which a relative adjustment of the crankshaft and camshaft with respect to one another, and thus a variation of the valve timing, is also performed as a function of the operating state of the internal combustion engine. The “VTEC” (Honda) adjustment device exists in different variants which have in common the fact that a switch between different actuation characteristics takes place as a function of certain parameters of engine operation. In the “Ti-VCT” (Ford) adjustment device, adjustment by means of hydraulic actuators is provided. The adjustment is performed in a continuously variable fashion as a function of engine load by means of electronic characteristic-map-based control. The three abovementioned adjustment devices are controlled in each case by an electronic engine control unit which also actuates the fuel injectors for the injection of predefined amounts of fuel. It is however also possible for such valve drive adjustment devices to be actuated autonomously, or by means of a control device which is independent of the actual engine control unit, during engine operation. Conceivable for this purpose are for example hydraulic actuators (charged for example with engine oil pressure), pneumatic actuators or for example centrifugal force adjusters (for example for crankshaft rotational speed dependency).
The known valve drive adjustment devices may furthermore be divided into two categories with regard to variability of adjustment, specifically discontinuously variable systems and continuously variable systems.
A discontinuously variable system may for example be constructed such that a plurality of different profiles per valve is provided on the camshaft. Each profile results in a different lift curve for the valve, wherein at all times only one profile can be active, and switching between the different profiles can be performed. In concepts of said type, a change in the lift curve is performed abruptly.
In relation thereto, continuously variable systems offer more comprehensive variability of the valve drive. Since said systems permit a continuous variation of the valve actuation characteristic, they thus eliminate for example the difficulties that otherwise result from an abrupt switch. Continuous systems are used in particular for low-loss load control of internal combustion engines. It is for example possible for the air or mixture supply to the combustion chamber to be controlled by means of the variability of the lift curve of an inlet valve.
In particular in the case of discontinuously variable systems which thus provide an abrupt switch between different actuation characteristics, a corresponding change in the parameters used for the control of the engine should, for optimum control of the combustion, take place equally abruptly. Such parameters include for example the parameters used for the predefinition (calculation) of the amounts of fuel to be injected and/or of the injection times and crank angles. To be able to switch the engine control at the “correct time”, the control unit however requires reliable information regarding the present switching state of the valve drive adjustment device. Said information must be kept permanently “up to date” and/or correspondingly updated upon a change in the switching state. If a switch of the valve drive adjustment device takes place for example at an arbitrary time during sequential operation of a multi-cylinder internal combustion engine, the changed predefinition of the parameters should thus ideally take effect immediately for the engine control operations following said time, in particular for the relevant control process (for example ignition, injection etc.) of the “next cylinder” (in the operating sequence) at the latest. Precise information regarding the switching state of the valve drive adjustment device is thus required in order to optimally control the combustion.
Such information could duly be obtained by means of a position sensor installed on the valve drive adjustment devices, which position sensor outputs to the control unit a position sensor signal representing the present switching state of the adjustment device.
Such a position sensor signal could then be taken into consideration by the electronic engine control unit as input information for the determination of the switching state of the valve drive adjustment device.
The arrangement of a position sensor on the valve drive adjustment device would however disadvantageously entail a certain amount of outlay in terms of construction, in particular if it were sought for the sensor signal output by said position sensor to represent the actual present switching state with high accuracy.